createCanvas(400, 400);

}

​

let xPos = 0;

let xSpeed = 4;

let xDir = 1;

let cRadius = 30;

​

function draw() {

  background(220, 0, 120);

  ellipse(xPos, height / 2, 2 * cRadius);

​

  xPos = xPos + xDir * xSpeed;

​

  if (xPos > width - cRadius) {

    xDir = -1;

  } else if (xPos < cRadius) {

    xDir = 1;

  }

}

​